It is well established that most of the tar and nicotine products can be removed from cigarette smoke by the use of a cigarette holder arranged so that those materials are condensed out of the smoke before it reaches the outlet opening of the holder and the smoker. It is possible to remove almost any selected percentage of those materials. Thus, to the extent that cigarette smoking can be made more safe, or less likely to be injurious to the smoker's health, the creators of tar and nicotine filtering apparatus can achieve almost any degree of safety of freedom from injury. However, to create such an apparatus which smoker's will attempt to use and will continue to use has proven to be a much more difficult task.
The acceptance of cigarette smoke filtering devices appears to be the function of three variables. The first is the degree of inhalation suction required to use the device. Another variable is the taste of the smoke, or the "strength" or "weakness" of the smoke. The last is the smoker's motive in using the filtering device. Acceptance of cigarette smoke filtering apparatus diminishes as the degree of inhalation suction increases significantly beyond what is required for normal cigarette smoking. Further, the use of cigarette smoke filtering apparatus diminishes if the smoke that reaches the smoker tastes significantly different from the taste of unfiltered cigarette smoke. Taste appears to be a function both of the composition of the smoke and of its temperature. If the smoker's motive is to remove part of the nicotine and tar content of the smoke so that he can continue the smoking habit with less likelihood of injury to himself, he may be willing to put up with a change in inhalation suction requirement and taste sufficiently long so that he becomes accustomed to the changed condition. On the other hand, the smoker whose objective is to rid himself of the smoking habit, and who believes that he must have a means for withdrawing by degrees, is likely to be less tolerant of changes in taste and suction requirements. It is easy to condense out the tars and nicotines produced by reducing the temperature of the smoke, but temperature reduction translates into a change in taste. While less easy, it is possible to remove tars and nicotine by utilizing the fact that the tar and nicotine products have greater mass than does the smoke and can be removed by increasing their kinetic energy to the point where they cannot change direction with the same facility as can the lighter smoke. However, increasing kinetic energy of the solid and semi-solids of the smoke requires that they be accelerated at the cost of increase in inhalation suction.
A number of prior art filters and smoker's withdrawal kits have sought to combine these two approaches in an effort to find an acceptable compromise between degradation of taste and increase in inhalation suction requirement. Finding an appropriate compromise is not merely a matter of balancing those two variables. Since normal suction pressure, the suction pressure that is required in the absence of any filtering apparatus, varies greatly during each "puff" or inhalation event, the amount of inhalation suction that is required during an inhalation event can be modified by the provision of smoke storage areas in the flow path through the filtering apparatus and its supporting structure.
An examination of the prior patents in this field will disclose that there are a variety of structures that can be used to cool and accelerate and decelerate and store smoke. Unfortunately, the thermal and aero-dynamic and hydraulic problems are sufficiently complex so that creating new filtering systems requires far more than creating new combinations of old features. Effective filters exist, but there is a need for new structures. That need arises out of the need to make them more useful in terms of the ease with which they can be kept clean, the cost of their production, and the security they provide against any trapped solids or liquids reaching the smoker's end of the device.